The overall objectives of the proposed research are (1) to refine models of potential exposures for use in environmental epidemiology that are derived from Geographical Information Systems (GIS) and (2) to assess the feasibility of application of the novel exposure indices to a case-control study of childhood cancers in the Southwestern Pennsylvania region. The proposed research will be accomplished under the following specific aims: (1) a GIS-based, index of potential exposure from hazardous sources will be refined for use in new and ongoing environmental epidemiology studies. The novel approach uses directionally-dependent wind rose frequencies and wind velocity in various combinations with toxic emission quantities, emission toxicities and frequencies to calculate an index of potential exposure from hazardous sources. (2) The potential exposure indices will be calculated for administrative regions (census tracts and blocks) in Southwestern Pennsylvania and compared with the indices calculated for iso-density population centers and randomly distributed regions. (3) Stand -alone algorithms will be created for use with GIS databases centered on other regions of interest identified using the GIS-based Atlas of Cancer. (4) A concurrent feasibility study for childhood cancer in a six-county region of Southwestern Pennsylvania will be performed. This portion of the study will determine the accessibility of relevant information for hospital-based cases and controls in the six-county region and develop the necessary mechanisms for mounting a full-scale case-control study using the novel potential exposure indices. The GIS-derived potential exposure indices derived in this research can be geographically referenced for use in GIS-based health studies in general and also directly linked with the coordinates of individual cases and controls in specific studies of disease. When the exposure estimates are coupled with geographically-reference health data, such as published in the Atlas of Cancer, this will crate an effective tool for (1) screening studies linking environmental exposures with disease and (2) providing a relative exposure measure for individuals in case-control studies of disease. Overall, the simplified potential exposure indices will improve both environmental epidemiological studies and the monitoring for purposes of disease control.